Readily adjustable snap-action switch



Nov. 17, 1964 E. J. KUDALls 3,157,759

READILY ADJUSTABLE SNAP-ACTION SWITCH Filed Jan. l5, 1963 i INVENTOR. 4x!" EW//V' a H04L/s,

.Y BY

United States Patent Oflice 3l57ji59 Patented Nov. 17, 1964 3,157,759 READILY ADJUSTABLE SNAP-ACTEQN SWETQH Edwin 3. Kudaiis, 504 Busse Road, Mount Prospect, lil. Filed Jan. 15, 1963, Ser. No. 251,631 14 Elairns. (Cl. 20d-67) This invention relates to electrical switches of the snap action type, and in particular to miniature switches known as microswitches, small in size, and highly sensitive to movements within an extremely short range of tolerable distance. Such switches are used in many military and industrial applications, :and are usually surrounded by some sort of mechanical linkage, adapting them to a particular application. This linkage may be such that the switch will respond to certain rotational movement of a shaft, or to a straight line movement, and in doing so, be responsive to a force of predetermined magnitude. This represents precision work, in which the unit must often respond, repeatedly, to movements within 0.001 inch, or within a fraction of a degree of rotational movement.

Existing switches must be selected to meet exact characteristics, in order to function properly in their intended environment, and if the demands are extremely critical, the linkage must be made to very exacting standards, and often adjustments must be included in the linkage to overcome the shortcomings.

It is therefore an `object of the present invention to provide a switch, with adjustment features adapted to overcome the said shortcomings in a superior manner.

Three basic characteristics of these sensitive switches are known las the Movement Differential, the Operating Point, and the Operating Force. The first is delined as the distance the actuator button, or plunger, must travel, in its retrograted movement, away from the point of actuation, before the switching mechanism snaps back to its original position; the second is defined as the distance inward that the plunger must be depressed from its normal, outward position of rest, before the switch is snapped; and the third is defined as the force (usually in ounces) that must be yapplied to the plunger, in order to depress it to the operating point. It is a particular object of the invention to provide built-in adjustment means for each of these characteristics.

Yet another object is to provide for improved electrical conductance at the switch contacts, and in particular, it is an object to achieve this in a wiping action associated with the mechanism of the Operating Force adjustment, and also by reason of high contact pressure engendered by tension springs.

A still further object is to provide a spring-actuated, toggle-type switch, in which the main carriage of current is provided for, by means lother than the toggle springs, to enable the use of durable material in the spring.

A further object is to provide a spring-actuated toggle in which the spring action combines pure tension with laterally applied forces of deformation, and a related objected is to provide a helical spring with closely wound convolutions, to provide high restoration forces in lateral, bending deformation.

These and other ends, which will be readily apparent, are attained by the present invention, a preferred form of which is described in the following specification, as illustrated in the drawing, in which:

FIGURE 1 is a perspective view of the switch according to the present invention,

FIGURE 2 is a perspective View of the assembled switch of FIGURE l, but, enlarged in scale over FlG- URE 1, with one of the separable halves removed, to show interior parts,

FIGURE 3 is a sectional view, taken on the plane of the line 3 3 of FlGURE 2,

FIGURE 4 is a sectional view taken on the plane of the line 4 4 of FIGURE 2, and

FIGURE 5 is a bracketed view, in perspective, showing the inner moving parts of the switch, as exploded in three, mutually perpendicular directions.

Referring to the drawings by characters of reference, there is shown a snap-action switch unit contained in a housing 1?, of generally L-form, formed by two, inwardly concave, shell-like halves 12 and 14, having interlocking, rabbeted edges 16 and with an exterior meeting line 18, lying in a central plane. The housing parts, of electrically insulating material, such as Bakelite, or one of the more modern plastics, are shown as secured together by rivets Ztl, but may be secured by bolts, selftapping screws, cementing, or autogenuous Welding or other suitable means. The rivet openings in one part may be slightly enlarged to allow for slight misfit in the parts, and one of the through mounting holes provided in the two halves may be slightly elliptical, such as the hole 21, to allow for mismatching of openings in a part to which the switch will be attached.

ln a portion of the unit which may be referred to as the foot of the L, the container It) carries -a pair of exteriorly located electrically conducting terminals 22, Zd, associated, respectively, with the alternative positions of the switch, as will be seen, and at the end of what may be considered the leg of the l., the container carries a single, exterior, electrical terminal 26, representing a fixed connection (input) in the switch circuit. The terminals have the usual apertures 28, for soldering, bolting, or spring-fastening leads thereto.

The mountings for terminals 22, 24, are identical, and are associated with adjustment features for the contacts located within the housing, and each comprises an anchoring member having a central, cylindrical, reduced neck 30, received in a bore defined by mating, semi-circular openings in the housing parts 12 and 14.-, and square, end ilanges 32, 34, the former engaging the inner surface of the housing, and the latter received in a square, counter recess in the outer surface of the housing, to hold the anchoring member against turning. The anchoring member has a threaded, axial passage, receiving an adjusting screw 36, secured -by a nut 37, outwardly of terminal 22 or 2d, and on its inner end, a head 38, which is the main body of a switch contact, and carries a contacting, outer disc 40, the head being preferably of copper alloy, and the contact of silver alloy. The louter end of the screw 36 has a slot d2, for receiving a screw driver, and the size of the contact head 36 prevents its removal from the housing. The adjustability of the contacts provides for Movement Differential, dened above. The Operating Point is also controlled by this adjustment.

Cooperating with the adjustable contacts is a swingably movable contact d4 with a headed portion 46, the shank d4 being received in an opening in a flat, llipper arm 48, and secured by riveting or upsetting action. To facilitate its swinging movement, the iiipper arm 48 has a knifeedge 5l?, on the end opposite contact 44, which is fulcrumed in a V-groove 52 in a block 54, of electrically conducting material, such as a copper alloy, contained within the housing, and which is adjustable in position, in a manner to be set forth hereinafter, and which is capable of slight movement during switching action, for any given position of adjustment, and the basic switching action will therefore be rst described from the standpoint of a block which is substantially fixed in position.

As seen in Figure 2, the head 46 of contact 44 is normally in contact with portion 46 associated with the upper terminal Z2, and it will be understood that this may be either a closed or open circuit, depending upon the particular function for which the switch is employed, and similarly terminal 24 may be in a closed or open circuit.

In either case, in the normal position of the switch shown in Figure 2, the contact is held by means of a pair of tension coil springs 56, 58, each having a looped end 60 engaging a pin 62 with its ends carried in axially aligned, transverse bores in the housing parts 12, 14, and each having an opposite, looped end 64, received on trunnion pins 66 on opposite side edges of llipper arm 48. The end mountings of the springs are so located that a plane through pin 62 and trunnions 66 is angularly disposed with respect to the plane of tlipper arm 43, and lies above the line of pivoting of the knife edge S-l of the ipper arm. As a result, head 46 of the movable contact is continuously biased against the upper, fixed contact, and can only be removed therefrom by deliberate action. For most ellicient action yin an organization according to the present invention, the coil spring 56 is preferably closely coiled, so that the spring is possessed of tension with the successive spring convolutions in contact. Since the current through the switch will be carried by the block 54, rather than the actuating spring, as in conventional switches, the springs 56, S may be made of music wire, or stainless steel, which aliord long mechanical life, which is important when switches are operated with great frequency.

In prior art devices, a toggle action is obtained by moving the extreme end of a spring, such as the loop 6d in an arcuate path until the spring is aligned with the equivalent of the flipper arm 4S, after which it passes over center, dipping the contacts to the alternative setting. However, in the present case, the outer ends of the springs are fixed at all times, and the alignment of the toggle system is accomplished by a pressure applied laterally of the spring, intermediate its length. In this system, the excursion of the actuator spring over the center position does not result in a new position of rest, requiring a pull on the spring end to restore original conditions, since the spring remains over center only so long as the actuating pressure remains applied, and the spring and Contact return to their normal position upon release of the actuating force. The latter is applied by means of a plunger, or push button 68, of insulating material, which may be the same as that of housing parts 12, 14, and which in ordinary use `is adapted for contact and movement by moving parts of machinery, Work pieces, control devices, and the like elements.

The plunger 68 is preferably cylindrical, with a domed,

outer end 70, received in a bore 72 in the housing, defined by mating, semi-cylindrical grooves in the parts thereof, and having a headed portion 74 on its inner end, lodged in a counterbore 75', and retaining the plunger against withdrawal from the housing. The head 74 is of downwardly open, channel form, sized for a snug, sliding t along the top edge of conductor block 54, upon which it is mounted, in surrounding relation thereto, and in the position wherein the head contacts the bottom of the counterbore, the channel bottom is elevated above the top of block 54. This provides for axial movement, to and from the block S4.

The plunger, which is hollow, houses a compression spring 75. Spring 75 will be selected to provide a proper value for the operating force, and may be omitted in some cases of use. A pin 76, freely positioned in an elongate, vertical slot 78, extending transversely through the block, and located above the springs 56, 58, transmits movement of the plunger to the springs. Where it is desired to keep out dust, moisture, and other foreign matter, the plunger may be provided with an O-ring 8l), lodged in an annular, channel groove 82 in the bore 72.

From the structure thus far described, the general mode of action will be apparent. Upon downward movement of the plunger, the force is transmitted through pin 76 to the springs so that they are each bent into a form having two angularly disposed sections, about the line of contact as a vertex, with the angle increasing until the leftward segments are aligned with the plane of flipper arm 4S, after which the said leftward segments pass over center and the Contact 44 is brought down, lin a rapid, snap action into contact with the system of lower terminal 24. In `this position, a plane between pin 62 and trunnions 66 is still above the knife edge 59, and therefore, upon release of the pressure on plunger 68, the springs will straighten out, and the retraction of the springs will carry the contact 116 back to its original, upper position, closing the circuit to terminal 22. The action is distinctly superior to that of a toggle or flipper governed by springs in pure tension and not subject to sidewise bending forces, since the lateral forces are present in appreciable magnitude at the moment of passage over center, whereas in the case of the springs in pure tension, the component of spring force laterally of the flipper must rise gradually from zero, which involves a time lag. This is in addition to the aforementioned feature of automatic restoration of normal switch conditions.

In order to vary the tension in the flipper springs S6, 55, the block 5d is so mounted in the housing as to be slidably movable, generally longitudinally of the springs, and for this purpose, the housing parts are provided with cavities having a ceiling 84, and a door S6. The latter has a further cavity 88, receiving a boss on the lower edge of block 54, so as to provide limits for the sliding movement of the block. The extension of the springs, as occasioned through the block 54, is eitected by an adjustment screw 92, generally similar in its form and mounting to the screws 35, but having, instead of the contact disc 4G, a reduced end 94, centering the end of a compression spring 96, of conducting material, such as a beryllium-copper alloy, the other end of which bears against an end of block 54, in surrounding relation to a boss 98 on the block. The screw 92 is thus part of the fixed terminal of the switch, being in electrical contact with contacts 44, 46, through spring 96, block 54, and flipper 48. Thus, the passage of current is not through the tension springs, as in prior devices, and the parts which actually carry the current may be of relatively massive construction, for carrying currents which are sizeable, for the relatively small over-all dimensions of the switch. This also avoids embrittlement of the springs due to heating and permits use of more durable material. lt will be seen that tension of springs 56, 58, may be adjusted by turning screw 92, after loosening its lock nut 37. By this means, the Operating Force is adjusted. It should also be noted that all three lock nuts serve a dual purpose, in locking the adjusting screws, and in holding the terminals 22, 24, 26 in place. By the construction shown, it is also possible to orient the terminals throughout wide angles of adjustment, for judicious location in any given environment, or mode of use.

The yieldable or floating nature of the mounting of block 54 introduces an important mode of action into the system, by virtue of the movement of the block, due to yielding in both the tension springs and the compression spring 6, during depression of the plunger. This results in a wiping action of contacts 44 and 46, which not only provides a superior electrical contact, in any given cycle of operation, but also a repeated cleaning action which inhibits corrosion or other tarnishing of the contact surfaces.

By means of suitable cement, the switch may be made moisture-tight and dust-tight, except in cases where the need for access from time to time may appear.

A bore 1&0 may be provided through the casing halves, for mounting a bail-like, U-shaped operating lever or a bell crank (not shown) adapted to contact the plunger 68, in certain uses.

While a certain, preferred embodiment has been shown and described, various modifications will be apparent, in the light of this disclosure, and the invention should not, therefore, be deemed as limited, except insofar as shall appear from the spirit and scope of the appended claims.

I claim:

1. A snap-action switch comprising: a housing with separable components having a planar line of parting, with mating notches defining openings, two of said openings being axially aligned, and one of said openings axially perpendicular to said two openings; internally threaded, terminal posts having reduced, neck portions received in said openings;means to hold said posts against rotation; an adjusting screw threadedly mounted in each post; means to prevent withdrawal of said screws from said posts; electrical contact plates on the inner ends of the screws in said aligned openings; a terminal carried by each screw, externally of said housing; a lock nut on each said screw, and adapted to hold said terminals in place, in predetermined orientation, angularly of the axis of the screw; a block of electrically conducting material, mounted for sliding motion in said housing, generally parallel to the axis of the screw in said one of said openings; an electrically conducting compression spring between said latter screw and said block; said block having a groove in a face on the side opposite said spring; a flipper arm having a knife edge, bearing in said groove for swinging action about said groove as an axis; a pair of contacts on opposite sides of said arm, and adapted to alternately contact the respective, said contact plates, upon swinging of said arm; a pair of tension coil springs on opposite sides of said block, each having one end anchored to said housing, on one side of said groove, and the other end anchored to said arm, on thev other side of said groove; saidspring being small in diameter, in comparison to its length, and with adjacent convolutions in contact; said block having an elongate, laterally arranged, through opening, with its length generally transverse to said spring; a pin in said through opening and adapted to contact said tension springs medially of the length thereof, while moving laterally, lengthwise of said through opening; a plunger slidably mounted in said block, and having a forked head, adapted to straddle an edge of said block, and contact said pin on opposite sides thereof, for movement thereof, to apply bending force to said tension springs; and a compression spring arranged to resist inward movement of said plunger.

2. A device as in claim 1, said means to prevent withdrawal of said screws comprising headed portions on said screws, internally of said housing.

3. A device as in claim l, said means to hold said posts against rotation comprising flanges of varying radii, cooperating with mating openings in said housing.

4. A snap-action switch comprising: a housing with separable components having a planar line of parting,

with mating notches defining openings, two of said open- Y ings being axially aligned, and one of said openings axially perpendicular to said two openings; internally threaded, terminal posts having reduced, neck portions received in said openings; means to hold said posts against rotation; an adjusting screw threadedly mounted in each post; means to prevent withdrawal of said screws from said posts; electrical contact plates on the inner ends of the screws in said aligned openings; a terminal carried by each screw, externally of said housing; a lock nut on each said screw, and adapted to hold said terminals in place, in predetermined orientation, angularly of the axis of the screw; a block of electrically conducting material, mounted for sliding motion in said housing, generally parallel to the axis of the screw in said one of said openings; an electrically conducting compression spring between said latter screw and said block; said block having a groove in a face on the side opposite said spring; a ipper arm having a knife edge, bearing in said groove for swinging action about said groove as an axis; a pair of contacts on opposite sides of said arm, and adapted to alternately contact the respective, said contact plates, upon swinging of said arm; a pair of tension coil springs on opposite sides of said block; each having one end anchored to said housing, on one side of said groove, and the other end anchored to said arm, on the other side of said groove; said spring being small in diameter, in comparison to its length, and with adjacent convolutions in contact; said block having an elongate, laterally arranged, through opening, with its length generally transverse to said spring; a pin in said through opening and adapted to contact said tension springs, medially of the length thereof, while moving laterally, lengthwise of said through opening; and a' plunger slidably mounted in said block, and having a forked head, adapted to straddle an edge of said block, and contact said pin on opposite sides thereof, for movement thereof, to apply bending force to said tension springs.

5. A snap-action switch comprising: a housing having openings, two of said openings being axially aligned, and one of said openings axially perpendicular to said two openings; internally threaded, terminal posts having reduced, neck portions received in said openings; means to hold said posts against rotation; and adjusting screw threadedly mounted in each post; means to prevent withdrawal of said screws from said posts; electrical contact plates on the inner ends of the screws in said aligned openings; a terminal carried by each screw, externally of said housing; a lock nut on each said screw, and adapted to hold said terminals in place, in predetermined orientation, angularly of the axis of the screw; a block of electrically conducting material, mounted for sliding motion in said housing, generally parallel to the axis of the screw in said one of said openings; `an electrically conducting compression spring between said latter screw and said block; said block having a groove in a face on the side opposite said spring; a flipper arm having a knife edge, bearing in said groove for swinging action about said groove as an axis; a pair of contacts on opposite sides of said arm, and adapted to alternately contact the respective, said Contact plates, upon swinging of saidarm; a pair of tension coil springs on opposite sides of said block, each having one end anchored to said housing, on one side of said groove, and the other end anchored to said arm, on the other side of said groove; said spring being small in diameter, in comparison to length, and with adjacent convolutions in contact; said block having an elongate, laterally arranged, through opening, with its length generally transverse to said spring; a pin in said through opening and adapted to contact said tension springs, while moving laterally, lengthwise of said through opening; and a plunger slidably mounted in said block, and having a forked head, adapted to straddle an edge of said block, and contact said pin on opposite sides thereof, for movement thereof, to apply bending force to said tension springs.

6. A snap-action switch comprising: a housing having openings, two of said openings being axially aligned, and one of said openings axially perpendicular to said two openings; internally threaded, terminal posts having reduced, neck portions received in said openings; and adjusting screw threadedly mounted in each post; means to prevent withdrawal of said screws from said posts; electrical contact plates on the inner ends of the screws in said aligned openings; a terminal carried by each screw, externally of said housing; a lock nut on each said screw, and adapted to hold said terminals in place, in predetermined orientation, angularly of the axis of the screw; a blockfof electrically conducting material, mounted for sliding motion in said housing, generally parallel to the axis of the screw in said one of said openings; an electrically conducting compression spring between said latter screw and said block; said block having a groove in a face on the side opposite said spring; a flipper arm having a knife edge, bearing in said groove for swinging action about said groove as an axis; a pair of contacts on opposite sides of said arm, and adapated to alternately contact the respective, said contact plates, upon swinging of said arm; a pair of tension coil springs on opposite sides of said block, each having one end anchored to said housing, on one side of said groove, and the other end anchored to said arm, on the other side of said groove; said spring being small in diameter, in comparison to its length, and with adjacent convolutions in contact, said blocking having an elongate, laterally arranged, through opening, with its length generally transverse to said spring; a pin in said through opening and adapted to contact said tension springs, medially of the length thereof, while moving laterally, lengthwise of said through opening; and a plunger slidably mounted in said block, and having a forked head, adapted to straddle an edge of said block, and contact said pin on opposite sides thereof, for movement thereof, to apply bending force to said tension springs.

7. A snap-action switch comprising: a housing having openings, two of said openings being axially aligned, and one of said openings axially perpendicular to said two openings; internally threaded, terminal posts having reduced, neck portions received in said openings; an adjusting screw threadedly mounted in each post; electrical contact plates on the inner ends of the screws in said aligned openings; a terminal carried by each screw, externally of said housing; a lock nut on each said screw, and adapted to hold said terminals in place, in predetermined orientation, angularly of the axis of the screw; a block of electrically conducting material, mounted for sliding motion in said housing, generally parallel to the axis of the screw in said one of said openings; an electrically conducting compression spring between said latter screw and said block; said block having a groove in a face on the side opposite said spring; a flipper arm having a knife edge, bearing in said groove for swinging action about said groove as an axis; a pair of contacts on opposite sides of said arm, and adapted to alternately contact the respective, said contact plates, upon swinging of said arm; a pair of tension coil springs on opposite sides of said block; each having one end anchored to said housing, on one side of said groove, and the other end anchored to said arm, on the other side of said groove; said spring being small in diameter, in comparison to its length, and with adjacent convolutions incontact, said block having an elongate, laterally arranged, through opening, with its length generally transverse to said spring; a pin in said through opening and adapted to contact said tension springs medially of the length thereof, while moving laterally, lengthwise of said through opening; and a plunger slidably mounted in said block, and having a forked head, adapted to straddle an edge of said block, and contact said pin on opposite sides thereof, for movement thereof, to apply bending force to said tension springs.

8. A snap-action switch comprising: a housing having openings, two of said openings being axially aligned, and one of said openings axially perpendicular to said two openings; internally threaded, terminal posts having reduced, neck portions received in said openings; an adjusting screw threadedly mounted in each post; electrical contact plates on the inner ends of the screws in said aligned openings; a block of electrically conducting material, mounted for sliding motion in said housing, generally parallel to the axis of the screw in said one of said openings; an electrically conducting compression spring between said latter screw and said block; said block having a groove in a face on the side opposite said spring; a flipper arm having a knife edge, bearing in said groove for swinging action about said groove as an axis; a pair of contacts on opposite sides of said arm, and adapted to alternately contact the respective, said Contact plates, upon swinging of said arm; a pair of tension coil springs on opposite sides of said block, each having one end anchored to said housing, on one side of said groove, and the other end anchored to said arm, on the other side of said groove; said spring being small in diameter, in comparison to its length, and with adjacent convolutions in contact, said block having an elongate, laterally arranged,

through opening, with its length generally transverse to said spring; a pin in said through opening nad adapted to contact said ytension springs medially of the length thereof, while moving laterally, lengthwise of said through opening; and a plunger slidably mounted in said block, and having a forked head, adapted to straddle an edge of said block, and contact said pin on opposite sides thereof, for movement thereof, to apply bending force to said tension springs.

9. A snap-action switch comprising: a housing having openings, two of said openings being axially aligned, and one of said openings axially perpendicular yto said two openings; internally threaded, terminal posts having reduced, neck portions received in said openings; an adjusting screw threadedly mounted in each post; electrical contact plates on the inner ends of the screws in said aligned openings; a block of electrically conducting material, mounted for sliding motion in said housing, generally parallel to the axis of the screw in said one of said openings, an electrically conducting compression spring between said latter screw and said block; said block having a groove in a face on the side opposite said spring; a iiipper arm having a knife edge, bearing in said groove for swinging action about said groove as an axis; a pair of contacts on opposite sides of said arm, and adapted to alternately Contact the respective, said contact plates, upon swinging of said arm; a pair of tension coil springs on opposite sides of said block, each having one end anchored to said housing, on one side of said groove, and the other end anchored to said arm, on theother side of said groove; said block having an elongate, laterally arranged, through opening, with its length generally transverse to said spring; a pin in said through opening and adapted to contact said tension springs medially of the length thereof, while moving laterally, lengthwise of said through opening; and a plunger slidably mounted in said block, and having a forked head, adapted to straddle an edge of said block, and contact said pin on opposite sides thereof, for movement thereof, to apply bending force to said `tension springs.

l0. A snap-action switch comprising: a housing having openings, two of said openings being axially aligned, and one of said openings axially perpendicular to said two openings; internally threaded, terminal posts having reduced, neck portions received in said openings; an adjusting screw threadedly mounted in each post; electrical contact plates on the inner ends of the screws in said aligned openings; a block of electrically conducting material, mounted for sliding motion in said housing, generally parallel to the axis of the screw in said one 0f said openings; an electrically conducting compression spring between said latter screw and said block; said block having a groove in a face on the side opposite said spring; a fiipper arm having a knife edge, bearing in said groove for swinging action about said groove as an axis; a pair of contacts on opposite sides of said arm, and adapted to alternately contact the respective, said contact plates, upon swinging of said arrn; a pair of tension coil springs on opposite sides of said block, each having one end anchored to said housing, on one side of said groove, and the other end anchored to said arm, on the other side of said groove; said block having an elongate, laterally arranged, through opening, with its length generally transverse to said spring; a pin in said through opening and adapted to contact said tension springs medially the length thereof, while moving laterally, lengthwise of said through opening; and a plunger slidably mounted in said block, and adapted to contact said pin for movement thereof, to apply bending force to said tension springs.

ll. A snap-action switch comprising: a housing having openings, two of said openings being axially aligned, and one of said openings axially perpendicular to said two openings; internally threaded, terminal posts having reduced, neck portions received in said openings; an adjusting screw threadedly mounted in each post; electrical contact plates on the inner ends of the screws in said aligned openings; a block of electrically conducting material, mounted for sliding motion in said housing; an electrically conducting compression spring between said latter screw and said block; said block having a groove in a face on the side opposite said spring; a flipper arm having a knife edge, bearing in said groove for swinging action about said groove as an axis; a pair of contacts on opposite sides of said arm, and adapted to alternately contact the respective, said contact plates, upon swinging of said arm; a pair of tension coil springs on opposite sides of said block, each having one end anchored to said housing, on one side of said groove, and the other end anchored to said arm, on the other side of said groove; said block having an elongate, laterally arranged, through opening, with its length generally transverse to said spring; a pin in said through opening and'adapted to contact said tension springs medially of the length thereof, while moving laterally, lengthwise of said through opening; and a plunger slidably mounted in said block, and adapted to contact said pin for movement thereof, to apply bending force to said tension springs.

12. A snap-action switch comprising: a housing having openings, two of said openings being axially aligned, and one of said openings axially perpendicular to said two openings; internally threaded, terminal posts having reduced, neck portions received in said openings; an adjusting screw threadedly mounted in each post; electrical contact plates on the inner ends of the screws in said aligned openings; a block of electrically conducting material, mounted for sliding motion in said housing; an electrically conducting compression spring between said latter screw and said block; a flipper arm arranged for swinging movement about an axis associated with said block; a pair of contacts on opposite sides of said arm, and adapted to alternately contact the respective, said contact plates,

upon swinging of said arm; a pair of tension coil springs on opposite sides of said block, each having one end anchored to said housing, on one side of said axis, and the other end anchored to said arm, on the other side of said axis; said block having an elongate, laterally arranged, through opening, With its length generally transverse to said spring; a pin in said through opening and adapted to contact said tension spring medially of the length thereof, while moving laterally, lengthwise of said through opening; and a plunger slidably mounted in said block, and adapted to contact said pin for movement thereof, to apply bending force to said tension springs.

13. A snap-action switch comprising: a housing with a plurality of terminals; a block of electrically-conducting material mounted for'sliding movement in said housing; an arm swingably carried by said block, and adapted to alternately contact said terminals, a pair of tension springs connected to said arm, at a point apart from its axis of swing, and anchored to said housing on the other side of said axis; said block having an elongated opening; a pin in said opening and adapted to contact said springs at a point medially of its length, while moving transversely to its length in said opening, a plunger adapted to urge said pin into contact with said springs, and means to adjust the tension of said springs through sliding movement of said block; said means including a common terminal of the switch.

14. A device as in claim 13, said means including an electrically conductive, compression spring. 

13. A SNAP-ACTION SWITCH COMPRISING: A HOUSING WITH A PLURALITY OF TERMINALS; A BLOCK OF ELECTRICALLY-CONDUCTING MATERIAL MOUNTED FOR SLIDING MOVEMENT IN SAID HOUSING; AN ARM SWINGABLY CARRIED BY SAID BLOCK, AND ADAPTED TO ALTERNATELY CONTACT SAID TERMINALS, A PAIR OF TENSION SPRINGS CONNECTED TO SAID ARM, AT A POINT APART FROM ITS AXIS OF SWING, AND ANCHORED TO SAID HOUSING ON THE OTHER SIDE OF SAID AXIS; SAID BLOCK HAVING AN ELONGATED OPENING; A PIN IN SAID OPENING AND ADAPTED TO CONTACT SAID SPRINGS AT A POINT MEDIALLY OF ITS LENGHT, WHILE MOVING TRANSVERSELY TO ITS LENGTH IN SAID OPENING, A PLUNGER ADAPTED TO URGE SAID PIN INTO CONTACT WITH SAID SPRINGS, AND MEANS TO ADJUST THE TENSION OF SAID SPRINGS THROGH SLIDING MOVEMENT OF SAID BLOCK; SAID MEANS INCLUDING A COMMON TERMINAL OF THE SWITCH. 